This invention relates to a coin sorter for use in a vending machine or the like and, more particularly, to a coin sorter having a bridge circuit for examining the genuineness and kinds of coins inserter in the sorter.
One type of known coin sorter for use in a vending machine has a coin detecting coil that is disposed along a passage through which inserted coils roll on. The detecting coil is connected to one arm of a bridge circuit and fed with an AC voltage. An example of this prior art coin sorter is shown in FIG. 1, in which an AC bridge circuit 1 has arms comprising a coin detecting coil SC, fixed resistors R.sub.10 and R.sub.11, and a variable resistor R.sub.12 plus a variable coil L.sub.11, respectively. The coil SC produces an alternating magnetic field by being supplied with an AC voltage of a constant frequency from an oscillator O, which is connected between power terminals A and B of the bridge circuit 1. The detecting coil is shown consisting of an equivalent reactance L.sub.0 and an equivalent resistance R.sub.0. Connected in parallel with the bridge circuit 1 is a semi-bridge circuit 2 which consists of a fixed resistor R.sub.21, a variable resistor R.sub.22 and a variable coil L.sub.21. Since the resistances of the variable resistors R.sub.12, R.sub.22 of the circuits 1, 2 and the reactances of the variable coils L.sub.11, L.sub.12 of these circuits are adjusted so as to assume different values, respectively, this sorter is capable of separating coins into two different types. The output terminals C and E.sub.1 of the bridge circuit 1 and the output terminals C and E.sub.2 of the circuit 2 are connected to differential amplifiers 3 and 4, respectively, which are connected to the comparison inputs of comparator circuits 7 and 8, respectively, via rectifier circuits 5 and 6, respectively.
As known in the prior art, the bridge circuit is set such that it changes from balanced state to unbalanced state once because of a change in the reactance of the coin detecting coil SC which takes place when an acceptable coin passes the coil SC. This is next illustrated by referring to vector diagram of FIG. 2 showing changes in voltages appearing at terminals A, B, C and D of the bridge circuit 1.
Referring to FIG. 2, A, B, C and D indicate the potentials at terminals A through D, respectively, of the AC bridge circuit 1 of FIG. 1. Where the system is ready for insertion of a coin in standby state, when a predetermined voltage V.sub.0 is applied between the terminals A and B of the bridge circuit 1, the voltage potential at point D, between the equivalent reactance L.sub.0, and the equivalent resistance R.sub.0 of the coil SC, and the voltage potential at the terminal C, between the resistance R.sub.0 and the fixed resistor R.sub.10, are shown at points D and C, respectively, of FIG. 2, because reactance leads resistance by a phase angle of 90.degree..
If a coin of a first kind, for example, a ten cent coin, is placed at the position of the coil SC, the reactance of the coil SC varies in response to the coin and so the potentials at the terminals C and D change to C.sub.01 and D.sub.01, respectively. If a coin of a second kind such as a twenty-five cent coin is placed at the position of the coil SC, the potentials at the terminals C and D change to C.sub.02, and D.sub.02, respectively, because the reactance of the coil SC varies differently from the case of the ten cent coin on account of its different characteristics, including the coin material composition, diameter and thickness.
In this way, the reactance of the detecting coil SC changes in response to the characteristics of different coins. Therefore, the variable resistors R.sub.12, R.sub.22 and variable coils L.sub.11, L.sub.12 of the circuits 1, 2 are individually adjusted so that the potential at terminal E.sub.1 of the bridge circuit 1 assumes the voltage at point C.sub.01 of FIG. 2 and so that the potential at terminal E.sub.2 of the bridge circuit 2 assumes the voltage at point C.sub.02 of FIG. 2, and so that the bridge circuit 1 reaches its balanced state once when the ten cent coin passes the coil SC, while the bridge circuit 2 attains its balanced condition once when the twenty-five cent coin passes across the coil SC, for example.
Accordingly, when the bridge circuits 1 and 2 are balanced, the respective differential amplifiers 3 and 4 or rectifier circuits 5 and 6 deliver a zero output, which is used to examine the genuineness of each coin introduced. For this purpose, when the comparison inputs to the comparator circuits 7 and 8 do not reach their respective reference values COM.sub.1 and COM.sub.2, their respective comparators 7 and 8 deliver a single pulse.
Although the aforementioned coin sorter used in a conventional apparatus is able to examine the genuineness of each coin introduced and the kinds of accepted coins by making use of the balance state of each bridge circuit, the number of the semi-bridge circuits 2 must be increased with the number of different coins to be detected. This arrangement also requires that a countermeasure be provided to prevent mutual induction between the variable coils of each semi-bridge circuit. In addition, in cases where the coin detecting coils SC have different characteristics, very cumbersome operations are necessary to adjust all of the variable resistors and variable coils.